Grain Growth in Ti(C,N)‐Based Cermets During Liquid‐Phase Sintering

Abstract

Growth behavior of Ti‐based carbonitride ceramic grains in two high‐Mo Ti(C,N)‐based cermets with Ni and Ni–20Cr (wt%) binders was investigated during liquid‐phase sintering under vacuum at 1410°C, using DSC, XRD, SEM, AEM, and EDS. Grain growth occurred primarily through two‐dimensional nucleation and lateral growth. Most significantly, the grain growth kinetics followed the cubic law, which was controlled by the diffusion of dissolved mass through liquid Ni‐based binder phase. However, when Ni–20Cr (wt%) was used as metallic binder, the inner rim of ceramic grains with the typical core‐rim structure was seldom complete, and there were often some fine Ni‐rich and Mo‐rich speckles in their core. In Ni‐rich and Mo‐rich speckles, there were two kinds of microstructure: one consisted of Ni‐based superlattice phase, and the other consisted of Ti‐based carbonitride ceramic phase and unknown phases. The three‐dimensional thermodynamic equilibrium shape of Ti‐based carbonitride ceramic grains evolved from a {111}‐faceted and round ‐edged octahedron to a {111}‐faceted and sharp‐edged octahedron. In addition, the grain growth rate increased, which was mainly attributed to that the decrease of solid/liquid transformation temperature of Ni‐based binder phase led to the increase of the diffusion rate of dissolved mass through liquid Ni‐based binder phase.